An update failed or the site is stuck in maintenance mode

• Read the message on Settings > System Update. It names the problem (for example a folder that is not writable).
• WHBMP recovers an interrupted update by itself within a few minutes, as long as the cron job runs.
• To bring the site up now: php artisan up.
• To put the database back from the backup made before the update: php artisan whbmp:restore-database.

See Updating WHBMP and plugins.